The Dynamics of Small-Scale Turbulence Driven Flows

M. A. Beer and G. W. Hammett

Theory of Fusion Plasmas Workshop, Varenna, Sept. 1998

We investigate the dynamics of small-scale turbulence-driven sheared ExB flows in nonlinear gyrofluid simulations. The importance of these zonal flows in the regulation of the turbulence was shown in our early simulations[1,2,3] and has been widely confirmed. Most of these flows experience fast collisionless linear damping, but there is a residual non-Maxwellian component of the flow which is undamped[4] and scales with r/R. In our original treatment, we included collisionless damping terms which capture the fast collisionless damping of the damped components, but which do not accommodate the linearly undamped components. Here, we modify the gyrofluid closures to account for Pfirsch-Schluter heat flows. This modification allows a linearly undamped component of the ExB flows, and here we begin to assess its importance in nonlinear simulations. Our preliminary results indicate very near marginal stability zero-flux states can exist where the undamped zonal flows completely damp the turbulence, as shown in Ref. 5. But away from marginal stability, we find that retaining the undamped component of the flow has very little effect.

1. W. Dorland, Ph. D. thesis, Princeton University (1993).

2. G. W. Hammett, M. A. Beer, W. Dorland, S. C. Cowley, and S. A. Smith, Plasma Phys. Controlled Fusion 35, 973 (1993).

3. M. A. Beer, Ph. D. thesis, Princeton University (1995).

4. M. N. Rosenbluth and F. L. Hinton, Phys. Rev. Lett. 80, 724 (1998).

5. A. M. Dimits, D. E. Shumaker, W. M. Nevins, B. I. Cohen, and S. E. Parker, Sherwood Fusion Theory Conference (1998).